DESCRIPTION: This proposal concerns Kip3, a new kinesin identified from the yeast database which has been implicated in nuclear orientation prior to anaphase. Localization of Kip3 to astral tubules has been demonstrated. Extensive microscopy is planned to test the hypothesis that it is these astral tubules that serve to correctly orient the spindle. A variety of genetic screens are planned to find the proteins that may function to couple Kip3 to the cell cortex and thereby allow it to correctly orient the nucleus through its action on astral tubules. The interaction with tubules and with associated proteins will be explored biochemically.